Migrants sleep on the railroad tracks in Tenosique, Tabasco. Tenosique is the starting point for migrants who will travel on top of a freight train north to the border with the United States. They sleep on the tracks to be sure that they can hear, and feel, approaching trains and won't miss them. The trip for these migrants, mostly from Central America, has become increasingly dangerous over the past several years as Mexico's drug war has raged and kidnappings and killings of migrants has increased.